Motor vehicles with a thermal engine conventionally comprise an on-board electrical network comprising a battery, generally a 12 V battery, which is designed to supply the various items of equipment with electrical energy, in particular a starter, which is indispensable for ensuring the starting of the thermal engine. After the starting, an alternator which is coupled to the thermal engine ensures that the battery is charged with a rectifier.
Nowadays, the developments in power electronics make it possible to design an inverter/rectifier which supplies and controls a single reversible polyphase rotary electrical machine which advantageously replaces the starter and the alternator.
Initially, this machine, known as an alternator-starter, substantially had the purpose of fulfilling the functions of a generator and electric motor which were previously dedicated to the alternator and to the starter, and in addition to recuperate the braking energy, or to provide the thermal engine with additional power and torque.
For the purpose of increasing the power and improving the performance of the alternator-starter by increasing its operating voltage, whilst maintaining the possibility of using other standard equipment designed for a 12 V to 14 V supply, in particular the lead batteries, a so-called “14+X” or “micro-hybrid” architecture was developed, described for example in patent application FR2838576 by the company VALEO EQUIPEMENTS ELECTRIQUES MOTEUR.
This architecture thus consists of an electric power network which connects the alternator-starter to an electrical energy storage element which operates at a voltage higher than 14 V, and can reach 48 V, and of an electric service network which connects all the other items of equipment. The adaptation of the voltage levels between the two networks is ensured by a reversible direct/direct converter.
In a second stage, ecological considerations led to the design of reversible machines with power of approximately 8 to 16 kW, which is sufficient to drive the vehicle at low speed, for example in an urban environment.
Power levels of this type have been able to be obtained, whilst maintaining compact electrical machines, only by bringing the voltage of the electrical power network up to a value of approximately 60 V, which is far higher than the nominal voltage of conventional lead batteries, in a system described in particular in patent application FR2988926, also in the name of VALEO EQUIPEMENTS ELECTRIQUES MOTEUR.
In addition, power networks with voltages of up to 12 V can be implemented in an architecture which allows the vehicle to be driven at full speed by the electric motor )architecture of the so-called “full hybrid” type, in comparison with the previous so-called “mild-hybrid” architecture).
In an electrical supply system of this type, information needs to be exchanged between the two networks.
An electronic control unit is necessary in order to control the rectifier/inverter at the voltage of the electric power network, on the basis of information obtained from equipment at the voltage of the service network, in particular the control unit of the thermal engine in the mild-hybrid architecture. Conversely, information relating to the generator/starter must be transmitted to the equipment in the passenger space.
In an electrical supply system of this type, it is necessary to guarantee that at no time can a connection which is used for exchange of information be able to be used to exchange a power current.